This invention relates to an acceleration detector and, more particularly, to an acceleration detector for detecting knocking of an internal combustion engine.
A conventional acceleration detector for detecting knocking of an internal combustion engine comprises a housing adapted to be rigidly secured to an engine and an acceleration transducer assembly disposed within the housing for detecting the acceleration on the housing which represents knocking of the engine. The housing comprises a base and a cover securely connected together. The transducer assembly comprises a disc-shaped diaphragm and a piezoelectric element concentrically attached to the center of the diaphragm for sensing flexure thereof for generating a signal representative of the acceleration of the housing. The diaphragm is rigidly supported by the housing at its outer continuous circumference edge portion. Typically, the circumference edge portion is firmly clamped between edges of the base and the cover of the housing which are mechanically connected together by means of caulking.
The sensitivity of the acceleration transducer assembly comprising the diaphragm and the piezoelectric element is at its best at the resonance frequency f.sub.0 which is determined by the diameter and the thickness of the diaphragm and the piezoelectric element, whereupon the output from the transducer assembly is at its maximum. The resonance frequency f.sub.0 is an important characteristic of the acceleration detector and it is required that the deviation of the resonance frequency f.sub.0 from one detector to another is minimized.
Another important factor of changing the resonance frequency f.sub.0 of the acceleration transducer assembly is the accuracy of the concentric positioning of the piezoelectric element relative to the diaphragm. If the piezoelectric element is bonded to the diaphragm with their centers misaligned, the resonance frequency f.sub.0 deviates from one detector to another.
With the conventional acceleration detector as described above, the disc-shaped piezoelectric element is simply bonded to the circular diaphragm, so that they are quite easily attached at an eccentric position, making the deviation of the resonance frequency f.sub.0 large and frequent.